1. Field of the Invention
This invention relates broadly to a hand grip for a hand tool. More particularly, this invention relates to an ergonomic grip which redistributes forces and moments from the hand to the forearm. This invention also relates to hand tools incorporating the ergonomic hand grip.
2. State of the Art
According to the National Institute for Occupational Safety and Health (NIOSH), excessive force imposed on muscles may increase the potential for musculoskeletal injury and/or disorder. In addition, NIOSH cites numerous studies which indicate that even less than excessive force may predispose a person to musculoskeletal disorders and injuries, especially during repetitive activities or static activities performed with an awkward posture.
Hand held devices have been developed in numerous fields to assist with accomplishing specific manual tasks. Light agricultural devices such as spades and trowels are used to manually displace small amounts of soil for planting and gardening purposes. Spades are instruments intended to be forced into compressed earth and be strong enough to pry and lift out the earth from its settled position. Unlike a spade, which is intended to be used with the operator in the standing position, a trowel is intended for digging earth with the operator kneeling. Whether using a spade or trowel, however, implement application involves forcibly inserting the blade of the device into the compact earth and then prying the earth from its settled position.
Shovels are distinguished from spades in that the former are intended for use with uncompressed matter such as gravel, dirt, and snow. A common issue associated with shovels, spades and trowels is the manually imposed force required to pry an object mass of material loose from its settled position. One way to decrease the manual force required is to increase the length from the working end of the implement to that of the manually applied force, i.e. to increase the moment arm. A common way to increase the moment arm is to increase the length of the shaft connecting the tool to its handle. For spades and shovels, the length of the shaft is usually limited by the height of the individual using the implement. Thus, it may still be necessary to use both hands to provide enough force to the handle of a spade or shovel to displace the object mass. Once the mass is freed, one of the operator's hands can grab hold of the shaft to act as a fulcrum for lifting or turning over the handled material.
There are some hand tools which are intended for use with the object mass close to the body simply because the object's load is too great. Such is the case in the field of haying, and that of butchering for the handling of an animal carcass. Butchering hooks are basically derivatives of logging and haying hooks.
Manual devices can also be used to manipulate living entities. The field of surgery often uses manual devices such as surgical retractors for holding or reflecting tissue matter to provide adequate exposure of an operative site. Hand held surgical retractors generally consist of a blade and an extended handle, the longitudinal axis of the handle generally being approximately ninety degrees relative to the longitudinal axis of the blade end. Commonly used hand-held surgical retractors possess a handle oriented in line with the retractor blade although some retractors allow the handle to be rotated 90°. The person performing the retraction may experience pain due to prolonged deviation of the wrist during time consuming procedures. In addition, awkward wrist positioning may induce painful fatigue of the arm and shoulder during long periods of time required for certain types of surgery. Furthermore, there may be instances when the assistant may not be positioned in the most optimum or efficient posture. This inadequate posture may lead to, among other things, finger, hand, wrist, elbow, shoulder and/or back fatigue increasing the risk of musculoskeletal disorder or injury to the assistant.
While the foregoing manual devices are generally useful for displacing a solid mass, the resultant force vector imposed upon the mass is primarily transferred through the hand/wrist of the user. The ligamentous and musculotendinous structures about the wrist must resist not only the load but also the rotation caused by the load. NIOSH has determined that there exists a direct correlation between certain tasks, hand and body posture during the performance of certain tasks, and various types of musculoskeletal disorders of the human wrist. Therefore, it would be beneficial to provide a manual device which would distribute, reduce and redirect the resultant loading vector acting upon the wrist. Further, in those situations where a manual force needed to be imposed upon a solid mass for any length of time while maintaining a certain posture (such as with a surgical retractor), such a device would reduce operator fatigue. Such a hand-held device would decrease the potential for musculoskeletal disorders and injuries of the wrist and hand.
U.S. Pat. No. 4,813,458 to Jacobucci discloses an ice, frost, and snow scraper for vehicle windscreens. The scraper has an ergonomic design with a center handle which acts as a fulcrum, and two lever arms which act as levers, which incurve and join each other to form the forearm rest at the rear extremity of the unit. The forearm rest sits on the user's forearm when using the device in a horizontal scraping direction. The device facilitates the act of cleaning winter elements off a windscreen or window through the use of leverage provided by the user's hand acting as a fulcrum and the user's forearm thus supplying the leverage necessary to create substantial downward pressure on the surface to be scraped. Unfortunately, Jacobucci's design causes forces to be concentrated in a very small and narrow region of the user's forearm very close to the wrist. This induces high contact stresses on the forearm.
U.S. Pat. No. 4,962,561 to Hamilton discloses a scraping device having a handle with a looped section which engages the upper forearm adjacent the elbow. The looped section has a curvature which accommodates a thick winter coat. The device enables the removal of ice and snow from windshields by transmitting the force of the upper forearm to the edge of the scraping device. Unlike Jacobucci's scraper, Hamilton's device distributes forces farther from the user's wrist. However, like Jacobucci, the forces are concentrated in a very small and narrow region of the user's forearm.
U.S. Pat. No. 5,832,563 to Simpson discloses a forearm assistant device which may be attached to almost any tool having a cylindrical shaft. The device has a frame which includes a cuff on one end so as to encircle the user's forearm adjacent to the elbow of the user. A handgrip extends from one side of the frame to the other side of the frame and is positioned approximately the length of the forearm from the elbow end of the frame. A tubular locking member is positioned on the other end of the frame for attaching it to the shaft of a hand tool. While the Simpson device spreads forces over a substantially larger area of the forearm and locates the forces far enough from the user's wrist, it is extremely awkward to use because it must be put on like an elbow length glove. Each time the tool is to be used, the entire forearm must be inserted through the cuff. When the tool is to be put down after use, the entire forearm must be pulled out of the cuff. These processes may require the use of both hands. As such, the Simpson forearm assistant is impractical for tools which are frequently picked up and put down such as garden tools.
U.S. Pat. No. 2,750,571 issued to Pfister, U.S. Pat. No. 5,471,698 issued to Francis et al., U.S. Pat. No. 5,890,259 issued to Sarac, and U.S. Des. Pat. No. D496,235 issued to Greene all provide a handle which is perpendicular to a straight or linear long axis of one or more structures on the side of the forearm. U.S. Pat. No. 5,455,981 to Weise, however, teaches a device which includes a handle which is parallel to the straight or linear long axis of dual side structures. U.S. Pat. No. 6,557,212 to Huang describes a devices having curved structures which merge to form a parallel handle, while U.S. Pat. No. 5,813,206 describes a device having a vertically upward extending handle which is perpendicular to the dual straight side rods.